1,3-dihalo-1,1,3,3-tetra(organyl)disiloxanes are used not only in the preparation of specific polysiloxanes but increasingly as protective group reagents in organic synthesis. Probably the most thoroughly investigated and most widely used disiloxanes of this class of substances are 1,3-dichloro-1,1,3,3-tetramethyldisiloxane and 1,3-dichloro-1,1,3,3-tetraisopropyldisiloxane.
These compounds can be prepared in principle by chlorinating 1,3-dihydro-1,1,3,3-tetra(organyl)disiloxanes. However, the chlorination processes described in the literature are generally unsuitable for scaling up to industrial production and also frequently have further disadvantages.
Thus, although the chlorination is possible in principle using elemental chlorine in the presence of a catalyst, for example according to JP-A-02145591, the substitution often takes place not only selectively at the desired silicon-bonded hydrogen but also at the organyl radicals. Purification of the desired molecule is often difficult and expensive.
The chlorination of 1,3-dihydro-1,1,3,3-tetramethyldisiloxane with copper(II) chloride in the presence of copper(I) iodide is described in EP-A-557 762 or the corresponding U.S. Pat. No. 5,258,535. Substantial disadvantages of this process are that at least one (mole) equivalent of copper(II) chloride is required per H--Cl exchange, and that considerable amounts of copper salts have to be handled, especially on an industrial scale. In addition, a solvent is required for the reaction.
Use of allyl chlorides is disclosed in DE-A-351 8605, of chlorohydrocarbons in JP-A-58004792, of acid chlorides in H. X. Zang et al., Synth. Commun. 17 (1987) 1299-1307, and of hypochlorites in R. Chawla et al., Synth. Commun. 29 (1999) 3499-3501, all generally in the presence of a specific catalyst for the chlorination of 1,3-dihydro-1,1,3,3-tetra(organyl)disiloxanes. Owing to the toxicological properties of these chlorinating agents, however, industrial use is problematic. Moreover, byproducts which have to be separated from the desired product by distillation are generated in these chlorination reactions.